Slice
A Slice Is a Slice
From a story in the New York Post called Walk Like a Local: How to Pass as a Native New Yorker:
When hunger strikes and you stop for pizza, keep vocabulary in mind. A "pie" is made up of "slices." You grab a "slice" on your way home from the bar but order a few "pies" if you're watching the Giants game with friends. Always preface your order with "lemmegetta," as in, "lemmegetta a slice." There is no need to specify plain cheese. That's what it means when you order a "slice."
Going further, I'd say that you'd complete the disguise by employing the "fold hold," folding the slice in half lengthwise for easier eating. (I believe Arthur "Food Maven" Schwartz and the pizza police call this "the libretto," because it's folded like a book.)